SpringMvc默认根据当前请求头中携带的区域信息locale来进行配置国际化.

WebMvcAutoConfiguration.WebMvcAutoConfigurationAdapter#localeResolver源码分析:

@Configuration@ConditionalOnWebApplication@ConditionalOnClass({ Servlet.class, DispatcherServlet.class,		WebMvcConfigurerAdapter.class })@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class,		ValidationAutoConfiguration.class })public class WebMvcAutoConfiguration {	// ...	// WebMvcAutoConfigurationAdapter	@Configuration	@Import(EnableWebMvcConfiguration.class) // 	@EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })	public static class WebMvcAutoConfigurationAdapter extends WebMvcConfigurerAdapter {		// ...		// LocaleResolver        @Bean		@ConditionalOnMissingBean        // 读取全局配置文件中的spring.mvc.locale区域信息进行国际化配置        // FIXED : Always use the configured locale.        // ACCEPT_HEADER: Use the "Accept-Language" header or the configured locale if the header is not set.		@ConditionalOnProperty(prefix = "spring.mvc", name = "locale")		public LocaleResolver localeResolver() {			if (this.mvcProperties					.getLocaleResolver() == WebMvcProperties.LocaleResolver.FIXED) {				return new FixedLocaleResolver(this.mvcProperties.getLocale());			}            // 如果全局配置文件中的spring.mvc.locale没有指定, 就根据请求头中的AcceptHeaderLocale获取区域信息, 进行国际化配置			AcceptHeaderLocaleResolver localeResolver = new AcceptHeaderLocaleResolver();			localeResolver.setDefaultLocale(this.mvcProperties.getLocale());			return localeResolver;		}	}}

AcceptHeaderLocaleResolver中根据Accept-Language中的区域信息来配置国际化.

public class AcceptHeaderLocaleResolver implements LocaleResolver {    private Locale defaultLocale;    public void setDefaultLocale(Locale defaultLocale) {		this.defaultLocale = defaultLocale;	}    public Locale getDefaultLocale() {		return this.defaultLocale;	}    // resolveLocale    @Override	public Locale resolveLocale(HttpServletRequest request) {		Locale defaultLocale = getDefaultLocale();        // 如果Accept-Language为空,就使用默认的国际化配置		if (defaultLocale != null && request.getHeader("Accept-Language") == null) {			return defaultLocale;		}		Locale requestLocale = request.getLocale();		if (isSupportedLocale(requestLocale)) {			return requestLocale;		}		Locale supportedLocale = findSupportedLocale(request);		if (supportedLocale != null) {			return supportedLocale;		}		return (defaultLocale != null ? defaultLocale : requestLocale);	}}

也可以在界面点击切换链接进行国际化切换，在切换链接后面指定国际化区域信息 /login.html?l=zh_CN

    中文    English

在WebMvcConfigurerAdapter中扩展自定义 LocaleResolver

@Configurationpublic class MyMvcConfig extends WebMvcConfigurerAdapter {    // ...    // 使用自定义的MyLocaleResolver    @Bean    public LocaleResolver localeResolver() {        return new MyLocaleResolver();    }}public class MyLocaleResolver implements LocaleResolver {    @Override    public Locale resolveLocale(HttpServletRequest request) {        // 获取/login.html?l=zh_CN中的请求参数l        String l = request.getParameter("l");        Locale locale = null;        if (!StringUtils.isEmpty(l)) {            String[] sp = l.split("_"); // en_US zh_CN            locale = new Locale(sp[0], sp[1]); // language，country        } else {            // 这里必须默认初始化一个bean，如果将该国际化配置到springBoot中，第一次进入界面调用国际化组件没有参数l，返回null，会报空指针            locale = new Locale("zh", "CN");        }        return locale;    }    @Override    public void setLocale(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Locale locale) {    }}

重启应用后，访问 http://localhost:8082/boot1/index.html, http://localhost:8082/boot1/index

点击【中文 English】链接切换国际化, 地址栏变化http://localhost:8082/boot1/index.html?l=en_US

开发期间thymeleaf模板引擎页面修改后要实时生效， 可以在全局配置文件禁用缓存

#禁用缓存spring.thymeleaf.cache=false

8. RestfulCRUD

8.1 拦截器

登录提交的校验可以使用拦截器, 下面我们写一个拦截器, 来实现如果用户没登录就不允许访问/main.html

public class LoginHandlerIntercepter implements HandlerInterceptor {        @Override    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {        Object loginUser = httpServletRequest.getSession().getAttribute("loginUser");        System.out.println("拦截器登录校验 loginUser=" + loginUser);        if (loginUser == null) {            // 没有登录，返回登录页面            httpServletRequest.setAttribute("msg", "没有权限，请先登录");       httpServletRequest.getRequestDispatcher("/index.html").forward(httpServletRequest, httpServletResponse);            return false;        }        // 已经登录，放行        return true;    }    @Override    public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {    }    @Override    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {    }}

在配置类中扩展SpringMvc的功能, 增加拦截器.

@Configurationpublic class MyMvcConfig extends WebMvcConfigurerAdapter {        // 添加自定义url映射视图关系    @Bean    public WebMvcConfigurerAdapter webMvcConfigurerAdapter() {        WebMvcConfigurerAdapter adapter = new WebMvcConfigurerAdapter() {            @Override            public void addViewControllers(ViewControllerRegistry registry) {                registry.addViewController("/").setViewName("login");                registry.addViewController("/index.html").setViewName("login");                // /main.html请求会映射到dashboard.html界面                registry.addViewController("/main.html").setViewName("dashboard");            }			// 添加拦截器            @Override            public void addInterceptors(InterceptorRegistry registry) {                // 	public static final String DEFAULT_METHOD_PARAM = "_method";	private String methodParam = DEFAULT_METHOD_PARAM;		public void setMethodParam(String methodParam) {		Assert.hasText(methodParam, "'methodParam' must not be empty");		this.methodParam = methodParam;	}	@Override	protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)			throws ServletException, IOException {		HttpServletRequest requestToUse = request;		// 如果表单提交的是post请求，进入转换逻辑		if ("POST".equals(request.getMethod()) && request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) == null) {            // 读取_method参数的值			String paramValue = request.getParameter(this.methodParam);            // 判断_method值非空			if (StringUtils.hasLength(paramValue)) {                // 将_method值替换到HttpServletRequest中，实现修改http请求方式的效果				requestToUse = new HttpMethodRequestWrapper(request, paramValue);			}		}        // 过滤器继续执行，HttpServletRequest替换成了包装过的requestToUse		filterChain.doFilter(requestToUse, response);	}		private static class HttpMethodRequestWrapper extends HttpServletRequestWrapper {		private final String method;		public HttpMethodRequestWrapper(HttpServletRequest request, String method) {			super(request);            // 初始化将外部传入的_method值给到HttpServletRequest#method			this.method = method.toUpperCase(Locale.ENGLISH);		}        // HttpMethodRequestWrapper父类实现了HttpServletRequest，重写getMethod方法, 最终映射handler读取的HTTP请求方式就是转换包装后的_method		@Override		public String getMethod() {			return this.method;		}	}}public class HttpServletRequestWrapper extends ServletRequestWrapper implements        HttpServletRequest {    // ...    private HttpServletRequest _getHttpServletRequest() {        return (HttpServletRequest) super.getRequest();    }        @Override    public String getMethod() {        return this._getHttpServletRequest().getMethod();    }    }

9. 错误处理机制

9.1 SpringBoot默认的错误处理机制

浏览器效果, 返回一个默认的错误页面

浏览器端发送请求的请求头中Accept中有text/html

Accept:text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*errorpublic String getServletPrefix() {	String result = this.servletPath;	if (result.contains("*")) {		result = result.substring(0, result.indexOf("*"));	}	if (result.endsWith("/")) {		result = result.substring(0, result.length() - 1);	}	return result;}// ErrorProperties#getPath  获取系统出现异常后,错误处理的url: /errorpublic class ErrorProperties {		@Value("${error.path:/error}")	private String path = "/error";	public String getPath() {		return this.path;	}}

9.2.3 BasicErrorController

当系统出现错误时, springboot会将去寻找处理错误的url (/error), 然后使用/error去找到mvc中映射的handler处理错误.

// 处理错误的handler,默认路由到 /error 来处理@Controller@RequestMapping("${server.error.path:${error.path:/error}}")public class BasicErrorController extends AbstractErrorController {	private final ErrorProperties errorProperties;    // AbstractErrorController#errorAttributes    private final ErrorAttributes errorAttributes;	// Create a new {@link BasicErrorController} instance.	public BasicErrorController(ErrorAttributes errorAttributes,			ErrorProperties errorProperties, List errorViewResolvers) {		super(errorAttributes, errorViewResolvers);		Assert.notNull(errorProperties, "ErrorProperties must not be null");		this.errorProperties = errorProperties;	}	@Override	public String getErrorPath() {		return this.errorProperties.getPath();	}    // 如果请求头中的Accept=text/html, 会在该方法中处理, 一般处理来自浏览器端的请求	@RequestMapping(produces = "text/html")	public ModelAndView errorHtml(HttpServletRequest request,			HttpServletResponse response) {        // 获取http-status		HttpStatus status = getStatus(request);        // 将异常信息封装到model中		Map model = Collections.unmodifiableMap(getErrorAttributes(				request, isIncludeStackTrace(request, MediaType.TEXT_HTML)));        // 设置http请求状态		response.setStatus(status.value());        // 解析model数据并返回view		ModelAndView modelAndView = resolveErrorView(request, response, status, model);		return (modelAndView == null ? new ModelAndView("error", model) : modelAndView);	}    // 其他客户端发送的请求，出现异常时使用该方法处理并产生Json类型的响应数据	@RequestMapping	@ResponseBody // response json	public ResponseEntity> error(HttpServletRequest request)         // 获取异常信息		Map body = getErrorAttributes(request,				isIncludeStackTrace(request, MediaType.ALL));		HttpStatus status = getStatus(request);		return new ResponseEntity>(body, status);	}	// Provide access to the error properties.	protected ErrorProperties getErrorProperties() {		return this.errorProperties;	}        // 从请求参数中获取请求状态 javax.servlet.error.status_code    protected HttpStatus getStatus(HttpServletRequest request) {		Integer statusCode = (Integer) request				.getAttribute("javax.servlet.error.status_code");		if (statusCode == null) {            // 500			return HttpStatus.INTERNAL_SERVER_ERROR;		}		try {			return HttpStatus.valueOf(statusCode);		}		catch (Exception ex) {            // 500			return HttpStatus.INTERNAL_SERVER_ERROR;		}	}        // 获取request中的请求参数    protected Map getErrorAttributes(HttpServletRequest request,			boolean includeStackTrace) {		RequestAttributes requestAttributes = new ServletRequestAttributes(request);        // DefaultErrorAttributes#getErrorAttributes		return this.errorAttributes.getErrorAttributes(requestAttributes,				includeStackTrace);	}}

9.2.4 DefaultErrorViewResolver

BasicErrorController#errorHtml中使用到了resolveErrorView进行错误处理的视图解析.

// 继承自AbstractErrorController的处理异常的视图解析器private final List errorViewResolvers;// BasicErrorController#resolveErrorViewprotected ModelAndView resolveErrorView(HttpServletRequest request,		HttpServletResponse response, HttpStatus status, Map model) {	for (ErrorViewResolver resolver : this.errorViewResolvers) {        // ErrorViewResolver#resolveErrorView 视图解析		ModelAndView modelAndView = resolver.resolveErrorView(request, status, model);		if (modelAndView != null) {			return modelAndView;		}	}	return null;}

DefaultErrorViewResolver#resolveErrorView

public class DefaultErrorViewResolver implements ErrorViewResolver, Ordered {	private static final Map SERIES_VIEWS;	static {		Map views = new HashMap();        // 按照请求状态码进行匹配 /error/4xx.html, /error/5xx.html		views.put(Series.CLIENT_ERROR, "4xx");		views.put(Series.SERVER_ERROR, "5xx");		SERIES_VIEWS = Collections.unmodifiableMap(views);	}	// ...		@Override	public ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status,			Map model) {		ModelAndView modelAndView = resolve(String.valueOf(status), model);		if (modelAndView == null && SERIES_VIEWS.containsKey(status.series())) {			modelAndView = resolve(SERIES_VIEWS.get(status.series()), model);		}		return modelAndView;	}	private ModelAndView resolve(String viewName, Map model) {        //  viewName是请求状态码, 拼接后/error/400.html 		String errorViewName = "error/" + viewName;        // 模板引擎可以解析这个页面地址的话, 就用这个页面地址封装视图  		TemplateAvailabilityProvider provider = this.templateAvailabilityProviders            // TemplateAvailabilityProviders#getProvider				.getProvider(errorViewName, this.applicationContext);		if (provider != null) {			return new ModelAndView(errorViewName, model);		}        // 模板引擎找不到对应的页面,就去类路径下去找		return resolveResource(errorViewName, model);	}	private ModelAndView resolveResource(String viewName, Map model) {        		for (String location : this.resourceProperties.getStaticLocations()) {			try {				Resource resource = this.applicationContext.getResource(location);				resource = resource.createRelative(viewName + ".html");				if (resource.exists()) {                    // 如果找到自定义的错误处理的页面,封装View					return new ModelAndView(new HtmlResourceView(resource), model);				}			}			catch (Exception ex) {			}		}		return null;	}	@Override	public int getOrder() {		return this.order;	}	public void setOrder(int order) {		this.order = order;	}		private static class HtmlResourceView implements View {		private Resource resource;		HtmlResourceView(Resource resource) {			this.resource = resource;		}		@Override		public String getContentType() {			return MediaType.TEXT_HTML_VALUE;		}        // 视图渲染		@Override		public void render(Map model, HttpServletRequest request,				HttpServletResponse response) throws Exception {			response.setContentType(getContentType());			FileCopyUtils.copy(this.resource.getInputStream(),					response.getOutputStream());		}	}}

TemplateAvailabilityProviders#getProvider

public class TemplateAvailabilityProviders {	// 配置的可用模板	private final List providers;	public TemplateAvailabilityProviders(ClassLoader classLoader) {		Assert.notNull(classLoader, "ClassLoader must not be null");        // 从spring.factories中加载Template availability providers //FreeMarkerTemplateAvailabilityProvider,ThymeleafTemplateAvailabilityProvider...		this.providers = SpringFactoriesLoader				.loadFactories(TemplateAvailabilityProvider.class, classLoader);	}		public TemplateAvailabilityProvider getProvider(String view, Environment environment,			ClassLoader classLoader, ResourceLoader resourceLoader) {		// ....		RelaxedPropertyResolver propertyResolver = new RelaxedPropertyResolver(				environment, "spring.template.provider.");		if (!propertyResolver.getProperty("cache", Boolean.class, true)) {            // findProvider 匹配模板			return findProvider(view, environment, classLoader, resourceLoader);		}		TemplateAvailabilityProvider provider = this.resolved.get(view);		if (provider == null) {			synchronized (this.cache) {				provider = findProvider(view, environment, classLoader, resourceLoader);				provider = (provider == null ? NONE : provider);				this.resolved.put(view, provider);				this.cache.put(view, provider);			}		}		return (provider == NONE ? null : provider);	}	private TemplateAvailabilityProvider findProvider(String view,			Environment environment, ClassLoader classLoader,			ResourceLoader resourceLoader) {		for (TemplateAvailabilityProvider candidate : this.providers) {            // 从候选模板中匹配可用的模板页面			if (candidate.isTemplateAvailable(view, environment, classLoader,					resourceLoader)) {				return candidate;			}		}		return null;	}}	

ThymeleafTemplateAvailabilityProvider#isTemplateAvailable

public class ThymeleafTemplateAvailabilityProvider		implements TemplateAvailabilityProvider {	@Override	public boolean isTemplateAvailable(String view, Environment environment,			ClassLoader classLoader, ResourceLoader resourceLoader) {		if (ClassUtils.isPresent("org.thymeleaf.spring4.SpringTemplateEngine",				classLoader)) {			PropertyResolver resolver = new RelaxedPropertyResolver(environment,					"spring.thymeleaf.");			String prefix = resolver.getProperty("prefix",					ThymeleafProperties.DEFAULT_PREFIX); // classpath:/templates/			String suffix = resolver.getProperty("suffix",					ThymeleafProperties.DEFAULT_SUFFIX); // .html            // classpath:/templates/404.html			return resourceLoader.getResource(prefix + view + suffix).exists();		}		return false;	}}

9.2.5 DefaultErrorAttributes

BasicErrorController解析浏览器端的请求或其他客户端请求的errorHtml和error的处理中都有获取异常相关信息的操作, 是从DefaultErrorAttributes中获取.

@Order(Ordered.HIGHEST_PRECEDENCE)public class DefaultErrorAttributes		implements ErrorAttributes, HandlerExceptionResolver, Ordered {	// ....    // 获取异常信息	@Override	public Map getErrorAttributes(RequestAttributes requestAttributes,			boolean includeStackTrace) {		Map errorAttributes = new LinkedHashMap();        // 存入时间戳		errorAttributes.put("timestamp", new Date());        // 存入响应状态码		addStatus(errorAttributes, requestAttributes);        // 存入异常信息		addErrorDetails(errorAttributes, requestAttributes, includeStackTrace);        // 存入请求uri		addPath(errorAttributes, requestAttributes);		return errorAttributes;	}	private void addStatus(Map errorAttributes,			RequestAttributes requestAttributes) {        // 获取异常的响应码javax.servlet.error.status_code的值		Integer status = getAttribute(requestAttributes,				"javax.servlet.error.status_code");		if (status == null) {			errorAttributes.put("status", 999);			errorAttributes.put("error", "None");			return;		}		errorAttributes.put("status", status);		try {			errorAttributes.put("error", HttpStatus.valueOf(status).getReasonPhrase());		}		catch (Exception ex) {			// Unable to obtain a reason			errorAttributes.put("error", "Http Status " + status);		}	}	private void addErrorDetails(Map errorAttributes,			RequestAttributes requestAttributes, boolean includeStackTrace) {		Throwable error = getError(requestAttributes);		if (error != null) {			while (error instanceof ServletException && error.getCause() != null) {				error = ((ServletException) error).getCause();			}			errorAttributes.put("exception", error.getClass().getName());			addErrorMessage(errorAttributes, error);			if (includeStackTrace) {				addStackTrace(errorAttributes, error);			}		}        // 获取异常信息javax.servlet.error.message的值		Object message = getAttribute(requestAttributes, "javax.servlet.error.message");		if ((!StringUtils.isEmpty(message) || errorAttributes.get("message") == null)				&& !(error instanceof BindingResult)) {            // 存入异常信息message			errorAttributes.put("message",					StringUtils.isEmpty(message) ? "No message available" : message);		}	}	private void addErrorMessage(Map errorAttributes, Throwable error) {		BindingResult result = extractBindingResult(error);		if (result == null) {			errorAttributes.put("message", error.getMessage());			return;		}		if (result.getErrorCount() > 0) {			errorAttributes.put("errors", result.getAllErrors());			errorAttributes.put("message",					"Validation failed for object='" + result.getObjectName()							+ "'. Error count: " + result.getErrorCount());		}		else {			errorAttributes.put("message", "No errors");		}	}	private void addPath(Map errorAttributes,			RequestAttributes requestAttributes) {        // 获取请求uri		String path = getAttribute(requestAttributes, "javax.servlet.error.request_uri");		if (path != null) {			errorAttributes.put("path", path);		}	}	@Override	public Throwable getError(RequestAttributes requestAttributes) {		Throwable exception = getAttribute(requestAttributes, ERROR_ATTRIBUTE);		if (exception == null) {			exception = getAttribute(requestAttributes, "javax.servlet.error.exception");		}		return exception;	}	@SuppressWarnings("unchecked")	private  T getAttribute(RequestAttributes requestAttributes, String name) {		return (T) requestAttributes.getAttribute(name, RequestAttributes.SCOPE_REQUEST);	}}

9.3 定制异常响应页面

9.3.1 有模板引擎的场景

将错误页面命名为 错误状态码.html放在模板引擎下的error文件夹下，发生此状态码的错误就会来到对应的页面。error/状态码.html；

我们可以使用4xx和5xx作为错误页面的文件名来匹配这种类型的所有错误，精确匹配优先(优先寻找精确的errorCode.html页面)。

// DefaultErrorViewResolver#SERIES_VIEWS, 保存请求出现错误时的默认处理页面前缀4xx 5xxprivate static final Map SERIES_VIEWS;static {    Map views = new HashMap();    views.put(Series.CLIENT_ERROR, "4xx");    views.put(Series.SERVER_ERROR, "5xx");    SERIES_VIEWS = Collections.unmodifiableMap(views);}// DefaultErrorViewResolver#resolveErrorView@Overridepublic ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status,		Map model) {    // 优先精确匹配, 错误响应状态码 404 ,500	ModelAndView modelAndView = resolve(String.valueOf(status), model);    // 如果精确匹配失败,就按照默认规则找4xx, 5xx	if (modelAndView == null && SERIES_VIEWS.containsKey(status.series())) {      // status.series()就是用错误响应状态码/100,返回匹配上的枚举, 查看HttpStatus.Series#valueOf       // 然后再从SERIES_VIEWS中获取是4xx还是5xx页面前缀		modelAndView = resolve(SERIES_VIEWS.get(status.series()), model);	}	return modelAndView;}private ModelAndView resolve(String viewName, Map model) {    // viewName就是精确匹配的错误响应状态码或默认匹配的4xx,5xx	String errorViewName = "error/" + viewName; // error/4xx    	TemplateAvailabilityProvider provider = this.templateAvailabilityProviders			.getProvider(errorViewName, this.applicationContext);	if (provider != null) {        // 模板解析完成后, 得到完整的异常处理页面路径 error/4xx.html 		return new ModelAndView(errorViewName, model);	}    // 如果模板引擎找不到, 就去"classpath:/META-INF/resources/", "classpath:/resources/",	// "classpath:/static/", "classpath:/public/" 去找 error/4xx.html 	return resolveResource(errorViewName, model);}

DefaultErrorAttributes使得页面能获取的信息：

• timestamp 时间戳

• status 状态码

• error 错误提示

• exception 异常

• message 异常消息

• path 请求url

/error/4xx.html页面

                                    
系统异常
        
time:[[(${#dates.format(timestamp,'yyyy-MM-dd HH:mm:ss')})]]
        
status:[[(${status})]]
        
error:[[(${error})]]
        
exception:[[(${exception})]]
        
message:[[(${message})]]
        
errors:[[(${errors})]]
        
trace:[[(${trace})]]
        
path:[[(${path})]]
    

启动应用后, 访问一个不存在的请求url, 如果没有提供精确匹配的404.html页面, 会继续匹配系统默认的4xx.html界面渲染异常信息.

如果提供了404.html页面, 就会优先精确匹配的404.html页面来渲染异常信息.

9.3.2 无模板引擎的场景

模板引擎找不到这个错误页面，就去静态资源文件夹下找。

"classpath:/META-INF/resources/""classpath:/resources/""classpath:/static/""classpath:/public/" "/" 当前项目的根路径

以上都没有错误页面，就来到SpringBoot默认的错误页面渲染异常信息。

具体源码在ErrorMvcAutoConfiguration中:

@Configuration@ConditionalOnProperty(prefix = "server.error.whitelabel", name = "enabled", matchIfMissing = true)@Conditional(ErrorTemplateMissingCondition.class)protected static class WhitelabelErrorViewConfiguration {	// 创建默认的异常渲染界面	private final SpelView defaultErrorView = new SpelView(			"
Whitelabel Error Page
"					+ "
This application has no explicit mapping for /error, so you are seeing this as a fallback.
"					+ "${timestamp}"					+ "There was an unexpected error (type=${error}, status=${status})."					+ "${message}");    // 异常渲染的viewBean	@Bean(name = "error")	@ConditionalOnMissingBean(name = "error")	public View defaultErrorView() {		return this.defaultErrorView;	}	// If the user adds @EnableWebMvc then the bean name view resolver from	// WebMvcAutoConfiguration disappears, so add it back in to avoid disappointment.	@Bean	@ConditionalOnMissingBean(BeanNameViewResolver.class)	public BeanNameViewResolver beanNameViewResolver() {		BeanNameViewResolver resolver = new BeanNameViewResolver();		resolver.setOrder(Ordered.LOWEST_PRECEDENCE - 10);		return resolver;	}}

9.4 定制异常响应Json

9.4.1 自定义异常处理

自定义用户不存在的异常类

public class UserNotExistException extends Exception {    public UserNotExistException(String message) {        super(message);    }}

模拟触发异常的请求, 只要访问/exception/username?username=aaa就会触发.

@RestController@RequestMapping(value = {"/exception"})public class ExceptionTestController {        @RequestMapping("/username")    @ResponseBody    public String user(@RequestParam("username") String username) throws UserNotExistException {        if ("aaa".equals(username)) {            throw new UserNotExistException("用户不存在！");        }        return username;    }}

使用全局异常处理类来捕获异常及异常处理.

package com.aiguigu.springboot02config.exception.handler;import com.aiguigu.springboot02config.exception.UserNotExistException;import org.springframework.web.bind.annotation.ControllerAdvice;import org.springframework.web.bind.annotation.ExceptionHandler;import org.springframework.web.bind.annotation.ResponseBody;import javax.servlet.http.HttpServletRequest;import java.util.HashMap;import java.util.Map;@ControllerAdvice(basePackages = {"com.aiguigu.springboot02config.controller"})public class MyExceptionHandler {    // 自定义异常处理    // 浏览器客户端都返回的json数据，无法实现自适应效果（浏览器返回页面，其他客户端返回json数据）    @ResponseBody    @ExceptionHandler(UserNotExistException.class)    public Map handleException(Exception e) {        Map map = new HashMap<>();        map.put("code", "user.not_exist");        map.put("message", e.getMessage());        return map;    }}

请求 http://localhost:8082/boot1/user?user=aaa ,浏览器和postman请求都返回自定义的json数据, 没有实现自适应响应效果。

{"code":"user.not_exist","message":"用户不存在！"}

9.4.2 自适应响应

可以将异常请求转发到/error进行自适应响应 , 在全局异常处理类中加入自定义异常信息并转发到/error. SpringBoot默认的异常处理请求就是 /error. (在BasicErrorController源码中查看.)

@ControllerAdvice(basePackages = {"com.aiguigu.springboot02config.controller"})public class MyExceptionHandler {	// 对UserNotExistException进行拦截处理    @ExceptionHandler(UserNotExistException.class)    public String handleException2(Exception e, HttpServletRequest request) {        Map map = new HashMap<>();        map.put("code", "user.not_exist");        map.put("message", "用户出错了. " + e.getMessage());                // 传入我们自己的错误状态码, 进入我们指定的错误页面        request.setAttribute("javax.servlet.error.status_code", 500);        // 转发到 /error 实现自适应效果（浏览器返回页面，其他客户端返回json数据） ErrorMvcAutoConfiguration        return "forward:/error";    }}

测试浏览器效果：

其他客户端请求效果：

{  "timestamp": 1682520309898,  "status": 500,  "error": "Internal Server Error",  "exception": "com.aiguigu.springboot02config.exception.UserNotExistException",  "message": "用户不存在！",  "path": "/boot1/exception/username"}

9.4.3 传递定制数据

请求出现异常后，会来到/error请求，会被BasicErrorController处理，响应数据是由getErrorAttributes得到的(父类AbstractErrorController的方法)；

• 编写一个ErrorController的实现类或AbstractErrorController的子类，放在容器中。

  • 异常响应数据是通过errorAttributes.getErrorAttributes方法得到的；容器中的DefaultErrorAttributes#getErrorAttributes()方法，默认进行数据处理。
  • 在全局异常处理类中将需要响应的定制异常信息存入到requst域中.

在全局异常处理类中将需要传递的信息保存到自定义字段ext中.

// 对UserNotExistException进行拦截处理@ExceptionHandler(UserNotExistException.class)public String handleException2(Exception e, HttpServletRequest request) {	Map map = new HashMap<>();	map.put("code", "user.not_exist");	map.put("message", "用户出错了. " + e.getMessage());		// 传入我们自己的错误状态码, 进入我们指定的错误页面	request.setAttribute("javax.servlet.error.status_code", 500);	// 将map信息存入自定义的ext字段	request.setAttribute("ext", map);	// 转发到 /error 实现自适应效果（浏览器返回页面，其他客户端返回json数据） ErrorMvcAutoConfiguration	return "forward:/error";}

自定义MyErrorAttributes，继承DefaultErrorAttributes，重写getErrorAttributes方法，响应数据map可以存入我们自定义的信息, 还能从request域对象中取出之前存入的信息ext。

// 给容器加入自定义的 ErrorAttributes@Componentpublic class MyErrorAttributes extends DefaultErrorAttributes {    // 返回值map就是页面和json能获取的所有字段    @Override    public Map getErrorAttributes(RequestAttributes requestAttributes, boolean includeStackTrace) {        Map map = super.getErrorAttributes(requestAttributes, includeStackTrace);        map.put("company", "atguigu");        // 我们的异常处理器携带的数据        Map ext = (Map) requestAttributes.getAttribute("ext", RequestAttributes.SCOPE_REQUEST);        map.put("ext", ext);        return map;    }}

浏览器测试效果

其他客户端测试效果, 返回了company, ext自定义字段信息.

{  "timestamp": 1682519269726,  "status": 500,  "error": "Internal Server Error",  "exception": "com.aiguigu.springboot02config.exception.UserNotExistException",  "message": "用户不存在！",  "path": "/boot1/exception/username",  "company": "atguigu",   "ext": {    "code": "user.not_exist",    "message": "用户出错了. 用户不存在！"  }}